The present invention is related to lightning strike detection and mapping systems, in general, and more particularly to a system capable of sampling input signal waveforms, generating a frequency spectrum therefrom, and displaying a representation of the frequency spectrum on the mapping display.
It is well known that thunderstorms present a serious threat to airborne craft as a result of the dangerous turbulence, up and down drafts, wind shear and other violent atmospheric disturbances generated thereby. Thunderstorms for the most part are comprised of clusters of cells which grow and dissipate within the storm through a variety of stages. Most of the violent atmospheric disturbance of the storm takes place during the mature stage of the storm cells. It was recognized by Paul Ryan an early pioneer in the field of weather mapping instrumentation that electrical discharges or lightning occurred coincidentally with the violent atmospheric disturbances during the mature stage of the storm cells. This strong correlation between the threatening atmospheric disturbances and electrical discharges was used by Ryan to create a weather mapping system known as Stormscope.RTM., which was disclosed in the U.S. Pat. No. 4,023,408 which is currently assigned to the same assignees as the instant application.
The Ryan system is capable of measuring pulse type electromagnetic radiation generated through the atmosphere from the large electric currents flowing within the lightning channel during a lightning stroke for the detection thereof. Ryan's system used an inverse relationship of the measured radiation to map the detected lightning strike on a display in range and bearing relative to an observation location which, for example, may be the location of the aircraft. In one embodiment, the observation location was calibrated at the center of the display screen and each displayed stroke appeared as a substantial point source at a bearing and radial dimension from the screen center, the radial dimension being proportional to the range measurement of the corresponding lightning stroke.
The dimension between the displayed stroke and screen center was not necessarily a measure of the actual range from the aircraft to the stroke but rather an approximation of range based on a mix of distance and intensity information of the detected lightning stroke. The Ryan system did not take into account the variety of lightning strikes, like return strikes, leader strikes and intra cloud strikes, nor did he utilize the different frequency and pulse width characteristics of these different strikes.
While the Ryan technology described by the aforementioned '408 patent has met and continues to meet a significant commercial need, further improvements are always desirable. For example, by classifying the detected lightning strike into a known type, the range and bearing measurements corresponding thereto may be more accurately estimated to narrow the statistical distribution thereof, thus rendering a more accurate range and bearing measurement over a given region for display mapping purposes.
From the teachings of Hans Volland in his edited text "CRC Handbook of Atmospherics", Vol. I, published by CRC Press, Inc. of Boca Raton, Fla. (1982), it is recognized that impulse forms of lightning currents may be characterized into different types by the spectral frequency and pulse width characteristics thereof. A Type 1 current is observed from lightning channel currents of return strikes and commonly referred to as aperiodic waveforms. A Type 2 current is observed from both return and intra cloud strikes and is referred to as damped oscillatory waves. And, Type 3 or K current is a special case of Type 2 and is sometimes referred to as the intermediate type. A more recent model of the Ryan Stromscope technology, referred to as WX-1000, manufactured by B.F. Goodrich FlightSystems, Inc. and marketed more than one year prior to the filing of the instant application, used pulse width measurements of the lightning strikes to discriminate intra cloud and leader strikes from the others.
In addition, a U.S. Patent bearing the number U.S. Pat. No. 4,672,305 issued to Coleman is directed to a lightning detection system which uses a ratio of low (1.5 kHz) and high (500 kHz) frequency magnetic field components to extend the range thereof. Further, U.S. Pat. No. 4,803,421 and its divisional counterpart U.S. Pat. No. 4,873,483 both issued to Ostrander and assigned to the same assignee as the instant application, are directed to lightning detection and mapping systems which determine lightning locations from the ratio of the integrated intensity of two different field components of lightning generated signals. Also, a data acquisition system for use in gathering lightning strike data is present in the paper "A Lightning Data Acquisition System", authorized by B. M. Stevens, Jr. et al. for the International Aerospace and Ground Conference on Lightning and Static Electricity at Dayton, Ohio, Jun. 24-26, 1986.
Because the electromagnetic radiation measurements of the lightning detection instrumentation are affected by noise and other unwanted interference, there is always the problem of false triggers causing unwanted processing of information. Accordingly, to avoid false triggering, the threshold trigger level for detecting valid lightning strikes may be set at higher magnitudes, although it recognized that the processing of lightning stroke signaling does not commence until the higher threshold level is reached. Since the past embodiments were analog, the pre-threshold portion of the incoming signal was lost. Consequently, the higher the threshold setting for false trigger avoidance, the greater the portion of incoming signal not being processed. Therefore, another area of improvement of the prior analog systems is the capability of avoiding false triggering without loss of a substantial initial portion of the incoming lightning signal.
Further, the prior lightning detection systems relied primarily on threshold triggering of the incoming lightning signal to commence processing thereof. Once processing began, it would continue for a predetermined processing interval until completion. There was no way to interrupt or abort information processing once started. Accordingly, if the processing was initiated by an invalid lightning stroke, such as a dart leader, a noise spike, or other interference, for example, a main or return stroke may be missed during the invalid processing interval and thus not measured. Accordingly, it is of paramount importance to be capable of distinguishing between valid and invalid lightning strikes early in the processing interval thereof so that the processing of an invalid strike may be aborted and the monitoring of incoming lightning signaling is quickly resumed. This capability would provide a greater opportunity to detect and measure the associated lightning strikes which follow quickly after their corresponding dart leaders.
Still further, the prior analog systems generally processed as much of the incoming lightning signaling as possible in performing correlation discrimination between the EH field measurements thereof. This method of correlation not only increased processing time but also processed signaling beyond the leading edge of the lightning pulse where noise became more prevalent in the incoming signal, thus corrupting at times the correlation discrimination. Thus, another area of improvement is the capability of limiting the correlation determination of the incoming lightning signaling to the leading edge thereof to effect an early correlation decision which accomplishes speeding up the processing time and avoiding significant noise disruption and interference that could render a false or corrupted correlation decision.
Another area of improvement over the past lightning detection systems is the capability of identifying ambient noise conditions which could interfere with weather mapping and/or lightning detection operations of the instrumentation. Even sporadic noise levels may cause false triggering or even false detection of invalid lightning strikes. An additional improvement is the capability of switching between weather mapping and noise or frequency spectrum identification modes for displaying such on a common weather mapping display. Accordingly, the operator or pilot could confirm the integrity of the instrumentation with the push of a button.
Still further, certain types of weather mapping displays require a backlight for viewing by an operator or pilot. In a cockpit environment, the ambient light levels tend to change as a result of varying the orientation of the aircraft Also, the brightness of the display is contrasted with the surrounding ambient light level of the cockpit. Thus, in order to maintain an even brightness level, the pilot or viewer will have to vary the backlight setting with each variation of ambient light condition. This could result in the pilot directing a substantial portion of his time controlling the brightness of the display rather than operating the aircraft. Accordingly, it is believed beneficial to have some hands-off automatic brightness level calibration for the display so that the pilot can direct his attention more to the flying of the aircraft.
Another area of improvement is directed to the integrity of the instrumentation in regard to the supply of power thereto. An operator or pilot utilizing a lightning detection system for storm avoidance may question the information being displayed on the display unit of the lightning detection system. Since, the aircraft instrumentation is generally powered by on board batteries, there is always the possibility of malfunctioning conditions and degradation of the battery voltage potential which could cause erroneous readings. Accordingly, it would be beneficial to the pilot to have the capability of reading the avionics power bus through the same lightning detection display without interrupting substantially the weather mapping operations. Thus, a malfunction or degradation of the avionics power bus could be quickly determined at the push of a button.